Operators of U.S. nuclear power plants are supposed to tell the NRC when pieces of equipment “contain defects that could create a substantial safety hazard,” regulations say. Although the report doesn’t assert that any imminent danger resulted from the lapses, many experts said the lack of communication could make it harder for other nuclear reactor operators to learn about flaws in their own equipment, because many similar parts are used in other reactors.

“If it happens in this one, maybe it’s a faulty part that’s in another plant and they should know,” said Diane Curran, a lawyer who has represented citizens groups and state and local governments in cases related to nuclear plants. “If you don’t report on this, the other licensees can’t look in their books and say, ‘Oh, do I have this one?’ and ‘Maybe I should switch it out.’ ”

The NRC inspector general’s report appeared at a time of heightened concern about nuclear safety as workers in Japan battled to control radiation leaks, fire, power outages and explosions at a series of reactors.

The inspector general’s office did not describe the defects, and that frustrated lawmakers, who said the report on unreported problems did not say what those problems were. Rep. Edward J. Markey (Mass.), the ranking Democrat on the House Natural Resources Committee, issued a statement saying that “this troubling study . . . raises serious questions about the self-policing allowed at nuclear facilities with regard to reporting of safety concerns.”

Markey said that “it is apparent that confusion and omissions regarding the reporting of defects at nuclear facilities are commonplace.” The inspector general blames the failures on uncertainty about when to report defects. Operators said they thought they needed to report only when an “event” took place and backup systems did not prevent a breakdown — or in bureaucratic lingo, an “actual loss of safety function.” In fact, the rules require them to report any defect, even if backup systems kicked in.

The inspector general said there was confusion about the rule among at least 28 percent of the nation’s 104 nuclear reactors, based on interviews done from mid-2009 to mid-2010. The IG’s report worried some experts who said the NRC was missing critical information that could prevent bigger accidents.

Paul Gunter, with the group Beyond Nuclear, said: “You could have two reactors that have faulty circuit breakers and though the part turns out to be defective, if it doesn’t necessarily cause an event like a reactor shutdown, it may be reported at one reactor, but not at another. But circuit breakers and fuses are . . . not trivial pieces of equipment.” The industry said its overall safety record is still laudable.

“We agree there’s room to clarify and simplify the regulations,” said Steve Kerekes, a spokesman for the Nuclear Energy Institute. “It’s important to keep in mind the broader picture here, which is that this particular reporting area is one sliver of a much broader regulatory regimen, which shows that U.S. nuclear plants are operating at very high levels of safety.”

The NRC said that the study focuses on a subset of defects caused by manufacturing and that the central issue is “administrative.” The agency said there are still other processes for catching and reporting defects. Separately, an employee for a subcontractor working at the Tennessee Valley Authority’s Watts Bar Nuclear Plant has been charged with lying about power system inspections, the Associated Press reported Thursday.

Prosecutors said Matthew David Correll, a 31-year-old electrician, lied last August about measuring cables that would supply power to a safety system at the reactor site. His attorney declined comment, the AP said.